Processes for preparing color stable red-emitting phosphors

ABSTRACT

Processes for preparing color stable red-emitting phosphors include contacting a complex fluoride phosphor of formula I with a first fluorine-containing oxidizing agent in gaseous form at a first temperature ranging from 200° C. to 700° C. to form a first product phosphor, contacting the first product phosphor in particulate form with a solution of a compound of formula II in aqueous hydrofluoric acid to form a treated phosphor, and contacting the treated phosphor with a second fluorine-containing oxidizing agent in gaseous form at a second temperature &lt;225° C.,
 
A x MF y :MN 4+   I
 
A x MF y   II
 
wherein A is independently at each occurrence Li, Na, K, Rb, Cs or a combination thereof, M is independently at each occurrence Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof, x is absolute value of the charge of the MF y  ion; and y is 5, 6 or 7.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application entitledPROCESSES FOR PREPARING COLOR STABLE RED-EMITTING PHOSPHORS filedconcurrently herewith under Ser. No. 15/197,897

BACKGROUND

Red-emitting phosphors based on complex fluoride materials activated byMn⁴⁺, such as those described in U.S. Pat. Nos. 7,358,542, 7,497,973,and 7,648,649, can be utilized in combination with yellow/green emittingphosphors such as YAG:Ce or other garnet compositions to achieve warmwhite light (CCTs<5000 K on the blackbody locus, color rendering index(CRI) >80) from a blue LED, equivalent to that produced by currentfluorescent, incandescent and halogen lamps. These materials absorb bluelight strongly and efficiently emit between about 610-635 nm with littledeep red/NIR emission. Therefore, luminous efficacy is maximizedcompared to red phosphors that have significant emission in the deeperred where eye sensitivity is poor. Quantum efficiency can exceed 85%under blue (440-460 nm) excitation.

One potential limitation in using Mn⁴⁺ doped fluoride hosts is theirsusceptibility to degradation under high temperature and humidity (HTHH)conditions. It is possible to reduce this degradation usingpost-synthesis processing steps, as described in U.S. Pat. Nos.8,252,613, 8,710,487, 8,906,724, and other patent applications assignedto General Electric Company. However, further improvement in stabilityof the materials is desirable.

BRIEF DESCRIPTION

Briefly, in one aspect, the present invention relates to a process thatincludes contacting a complex fluoride phosphor of formula I,A_(x)MF_(y):Mn⁴⁺  Iwith a first fluorine-containing oxidizing agent in gaseous form at afirst temperature ranging from about 200° C. to about 700° C., to form afirst product phosphor;

-   -   contacting the first product phosphor in particulate form with a        solution of a compound of formula II in aqueous hydrofluoric        acid,        A_(x)MF_(y)  II        to form a treated phosphor; and    -   contacting the treated phosphor with a second        fluorine-containing oxidizing agent in gaseous form at a second        temperature of less than 225° C.;

wherein

-   -   A is independently at each occurrence Li, Na, K, Rb, Cs, or a        combination thereof;    -   M is independently at each occurrence Si, Ge, Sn, Ti, Zr, Al,        Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;    -   x is the absolute value of the charge of the MF_(y) ion; and    -   y is 5, 6 or 7.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross-sectional view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a lighting apparatus inaccordance with another embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a lighting apparatus inaccordance with yet another embodiment of the invention;

FIG. 4 is a cutaway side perspective view of a lighting apparatus inaccordance with one embodiment of the invention;

FIG. 5 is a schematic perspective view of a surface-mounted device (SMD)backlight LED.

DETAILED DESCRIPTION

In the context of the present invention, the terms “complex fluoridematerial” “complex fluoride phosphor” and “complex fluoride compound”mean a coordination compound containing at least one coordination centersurrounded by fluoride ions acting as ligands, and charge-compensated bycounter ions as necessary. In one example, K₂SiF₆:Mn⁴⁺, the coordinationcenter is Si and the counterion is K. Complex fluorides are occasionallywritten as a combination of simple, binary fluorides but such arepresentation does not indicate the coordination number for the ligandsaround the coordination center. The square brackets (occasionallyomitted for simplicity) indicate that the complex ion they encompass isa new chemical species, different from the simple fluoride ion. The Mn⁴⁺activator ion also acts as a coordination center, substituting part ofthe centers of the host lattice, for example, Si. The host lattice,including the counter ions, may further modify the excitation andemission properties of the activator ion.

The amount of manganese in the Mn⁴⁺ doped phosphors of formula I rangesfrom about 1 mol % to about 30 mol %, particularly from about 3 mol % toabout 20 mol %. In embodiments where the phosphor formula I isK₂SiF₆:Mn⁴⁺, the amount of manganese ranges from about 1 mol % (about0.25 wt %) to about 25 mol % (about 6 wt %), particularly from about 2mol % (about 0.5 wt %) to about 20 mol (about 5 wt %), and moreparticularly from about 2 mol % (about 0.5 wt %) to about 4 wt % (about16.5 mol %).

In particular embodiments, the coordination center of the phosphor, thatis, M in formula I, is Si, Ge, Sn, Ti, Zr, or a combination thereof.More particularly, the coordination center is Si, Ge, Ti, or acombination thereof, and the counterion, or A in formula I, is Na, K,Rb, Cs, or a combination thereof, and y is 6. Examples of phosphors offormula I include K₂SiF₆:Mn⁴⁺, K₂TiF₆:Mn⁴⁺, K₂SnF₆:Mn⁴⁺, Cs₂TiF₆,Rb₂TiF₆, Cs₂SiF₆, Rb₂SiF₆, Na₂TiFe:Mn⁴⁺, Na₂ZrFe:Mn⁴⁺, K₃ZrF₇:Mn⁴⁺,K₃BiFe:Mn⁴⁺, K₃YFe:Mn⁴⁺, K₃LaFe:Mn⁴⁺, K₃GdF₆:Mn⁴⁺, K₃NbF₇:Mn⁴⁺,K₃TaF₇:Mn⁴⁺. In particular embodiments, the phosphor of formula I isK₂SiFe:Mn⁴⁺

In some embodiments, the phosphor is selected from the group consistingof

-   -   (A) A₂MF₅:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs, and        combinations thereof; and where M is selected from Al, Ga, In,        and combinations thereof;    -   (B) A₃MFe:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs, and        combinations thereof; and where M is selected from Al, Ga, In,        and combinations thereof;    -   (C) Zn₂MF₇:Mn⁴⁺, where M is selected from Al, Ga, In, and        combinations thereof;    -   (D) Aln₂F₇:Mn⁴⁺ where A is selected from Li, Na, K, Rb, Cs, and        combinations thereof;    -   (E) A₂MFe:Mn⁴⁺, where A is selected from Li, Na, K, Rb, Cs, and        combinations thereof; and where M is selected from Ge, Si, Sn,        Ti, Zr, and combinations thereof;    -   (F) EMFe:Mn⁴⁺, where E is selected from Mg, Ca, Sr, Ba, Zn, and        combinations thereof; and where M is selected from Ge, Si, Sn,        Ti, Zr, and combinations thereof;    -   (G) Ba_(0.65)Zr_(0.35)F_(2.70):Mn⁴⁺; and    -   (H) A₃ZrF₇:Mn⁴⁺ where A is selected from Li, Na, K, Rb, Cs, NH₄;        and combinations thereof.

Although the inventors do not wish to be held to any particular theoryto explain the improvement in color stability that can result fromsubjecting the phosphor to a process according to the present invention,it is postulated that the phosphor may contain defects such asdislocations, F⁻ vacancies, cation vacancies, Mn³⁺ ions, Mn²⁺ ions, OH⁻replacement of F⁻, or surface or interstitial H⁺/OH⁻ groups that providenon-radiative recombination pathways, and these are healed or removed byexposure to the oxidizing agent at elevated temperature.

In a first step of a process according to the present invention, acomplex fluoride phosphor of formula I is contacted with a firstfluorine-containing oxidizing agent in gaseous form at a firsttemperature to form a first product phosphor. The first temperatureranges from about 200° C. to about 700° C., particularly from about 350°C. to about 700° C. during contact, and in some embodiments from about500° C. to about 700° C. The phosphor is contacted with the oxidizingagent for a period of time sufficient to convert it to a color stablephosphor. Time and temperature are interrelated, and may be adjustedtogether, for example, increasing time while reducing temperature, orincreasing temperature while reducing time. In particular embodiments,the time is at least one hour, particularly for at least four hours,more particularly at least six hours, and most particularly at leasteight hours. In a specific embodiment, the phosphor is contacted withthe oxidizing agent for a period of at least eight hours at a firsttemperature of about 500° C.

The fluorine-containing oxidizing agent may be F₂, HF, SF₆, BrF₅,NH₄HF₂, NH₄F, KF, AlF₃, SbF₅, ClF₃, BrF₃, KrF, XeF₂, XeF₄, NF₃, SiF₄,PbF₂, ZnF₂, SnF₂, CdF₂, a C₁-C₄ fluorocarbon, or a combination thereof.Examples of suitable fluorocarbons include CF₄, C₂F₆, C₃F₈, CHF₃,CF₃CH₂F, and CF₂CHF. The In particular embodiments, thefluorine-containing oxidizing agent is F₂. The amount of oxidizing agentin the atmosphere may be varied to obtain the color stable phosphor,particularly in conjunction with variation of time and temperature.Where the fluorine-containing oxidizing agent is F₂, the atmosphere mayinclude at least 0.5% F₂, although a lower concentration may beeffective in some embodiments. In particular, the atmosphere may includeat least 5% F₂ and more particularly at least 20% F₂. The atmosphere mayadditionally include nitrogen, helium, neon, argon, krypton, xenon, inany combination with the fluorine-containing oxidizing agent. Inparticular embodiments, the atmosphere is composed of about 20% F₂ andabout 80% nitrogen.

The manner of contacting the phosphor with the fluorine-containingoxidizing agent is not critical and may be accomplished in any waysufficient to yield a color stable phosphor having the desiredproperties. In some embodiments, the chamber containing the phosphor maybe dosed and then sealed such that an overpressure develops as thechamber is heated, and in others, the fluorine and nitrogen mixture isflowed throughout the anneal process ensuring a more uniform pressure.In some embodiments, an additional dose of the fluorine-containingoxidizing agent may be introduced after a period of time.

In a second step, the first product phosphor produced in the first stepis contacted with a solution of a compound of formula II in aqueoushydrofluoric acid,A_(x)MF_(y)  IIto form a treated phosphor, as described in U.S. Pat. Nos. 8,252,613,8,710,487, and US 2015/0054400. In preferred embodiments, the solutionis saturated or nearly saturated. A nearly saturated solution is onethat contains 1-10% solvent in excess of the amount required to make asaturated solution. In one example, K₂SiF₆:Mn⁴⁺ is treated with a nearlysaturated solution K₂SiF₆ in aqueous HF prepared by adding approximately1-5 vol % aqueous HF to a saturated solution of K₂SiF₆ in aqueous HF.

The temperature at which the first product phosphor is contacted withthe solution is not particularly limited and may be selected accordingto convenience, although other parameters such as time or concentrationmay be adjusted at high or low temperatures to yield the desiredproperties of the phosphor. In particular embodiments, the temperatureranges from about 20° C. to about 50° C. The period of time required totreat the phosphor ranges from about one minute to about five hours,particularly from about five minutes to about one hour. Concentration ofhydrofluoric acid in the aqueous HF solutions ranges from about 20% w/wto about 70% w/w, particularly about 40% w/w to about 70% w/w. Lessconcentrated solutions may result in lower yields of the phosphor.

In a third step, the treated phosphor is contacted with a secondfluorine-containing oxidizing agent in gaseous form at a secondtemperature. The second temperature may the same as the firsttemperature, or may be less than the it, ranging up to and including225° C., particularly up to and including 100° C., and moreparticularly, up to and including 90° C. The time for contacting withthe oxidizing agent in the third step may be the same as the time forthe first step. In particular embodiments, the time is at least onehour, particularly for at least four hours, more particularly at leastsix hours, and most particularly at least eight hours. In a specificembodiment, the phosphor is contacted with the oxidizing agent for aperiod of at least eight hours at a temperature of about 90° C. Theoxidizing agent may be the same as or different from that used in thefirst annealing step. In particular embodiments, the fluorine-containingoxidizing agent is F₂. More particularly, the atmosphere may include atleast 20% F₂.

During the third step, the phosphor may be contained in a vessel havinga non-metallic surface in order to reduce contamination of the phosphorwith metals. In particular embodiments, the vessel and surface thereofis composed of a fluoropolymer. For example, a crucible or boat made ofpolytetrafluoroethylene may be used to contain the phosphor. Theresulting phosphor is dry and may have fewer hydroxide groups on thesurface of the particles. By reducing surface groups such as hydroxides,the degree of agglomeration may be reduced and correspondingly,decreased bulk density which may result in an improvement inmanufacturing.

A lighting apparatus or light emitting assembly or lamp 10 according toone embodiment of the present invention is shown in FIG. 1. Lightingapparatus 10 includes a semiconductor radiation source, shown as lightemitting diode (LED) chip 12, and leads 14 electrically attached to theLED chip. The leads 14 may be thin wires supported by a thicker leadframe(s) 16 or the leads may be self supported electrodes and the leadframe may be omitted. The leads 14 provide current to LED chip 12 andthus cause it to emit radiation.

The lamp may include any semiconductor blue or UV light source that iscapable of producing white light when its emitted radiation is directedonto the phosphor. In one embodiment, the semiconductor light source isa blue emitting LED doped with various impurities. Thus, the LED maycomprise a semiconductor diode based on any suitable III-V, II-VI orIV-IV semiconductor layers and having an emission wavelength of about250 to 550 nm. In particular, the LED may contain at least onesemiconductor layer comprising GaN, ZnSe or SiC. For example, the LEDmay comprise a nitride compound semiconductor represented by the formulaIn_(i)Ga_(j)Al_(k)N (where 0≤i; 0≤j; 0≤k and i+j+k=1) having an emissionwavelength greater than about 250 nm and less than about 550 nm. Inparticular embodiments, the chip is a near-uv or blue emitting LEDhaving a peak emission wavelength from about 400 to about 500 nm. SuchLED semiconductors are known in the art. The radiation source isdescribed herein as an LED for convenience. However, as used herein, theterm is meant to encompass all semiconductor radiation sourcesincluding, e.g., semiconductor laser diodes. Further, although thegeneral discussion of the exemplary structures of the inventiondiscussed herein is directed toward inorganic LED based light sources,it should be understood that the LED chip may be replaced by anotherradiation source unless otherwise noted and that any reference tosemiconductor, semiconductor LED, or LED chip is merely representativeof any appropriate radiation source, including, but not limited to,organic light emitting diodes.

In lighting apparatus 10, phosphor composition 22 is radiationallycoupled to the LED chip 12. Radiationally coupled means that theelements are associated with each other so radiation from one istransmitted to the other. Phosphor composition 22 is deposited on theLED 12 by any appropriate method. For example, a water based suspensionof the phosphor(s) can be formed, and applied as a phosphor layer to theLED surface. In one such method, a silicone slurry in which the phosphorparticles are randomly suspended is placed around the LED. This methodis merely exemplary of possible positions of phosphor composition 22 andLED 12. Thus, phosphor composition 22 may be coated over or directly onthe light emitting surface of the LED chip 12 by coating and drying thephosphor suspension over the LED chip 12. In the case of asilicone-based suspension, the suspension is cured at an appropriatetemperature. Both the shell 18 and the encapsulant 20 should betransparent to allow white light 24 to be transmitted through thoseelements. Although not intended to be limiting, in some embodiments, themedian particle size of the phosphor composition ranges from about 1 toabout 50 microns, particularly from about 15 to about 35 microns.

In other embodiments, phosphor composition 22 is interspersed within theencapsulant material 20, instead of being formed directly on the LEDchip 12. The phosphor (in the form of a powder) may be interspersedwithin a single region of the encapsulant material 20 or throughout theentire volume of the encapsulant material. Blue light emitted by the LEDchip 12 mixes with the light emitted by phosphor composition 22, and themixed light appears as white light. If the phosphor is to beinterspersed within the material of encapsulant 20, then a phosphorpowder may be added to a polymer or silicone precursor, loaded aroundthe LED chip 12, and then the polymer precursor may be cured to solidifythe polymer or silicone material. Other known phosphor interspersionmethods may also be used, such as transfer loading.

In some embodiments, the encapsulant material 20 is a silicone matrixhaving an index of refraction R, and, in addition to phosphorcomposition 22, contains a diluent material having less than about 5%absorbance and index of refraction of R±0.1. The diluent material has anindex of refraction of ≤1.7, particularly ≤1.6, and more particularly≤1.5. In particular embodiments, the diluent material is of formula II,and has an index of refraction of about 1.4. Adding an opticallyinactive material to the phosphor/silicone mixture may produce a moregradual distribution of light flux through the phosphor/encapsulantmixture and can result in less damage to the phosphor. Suitablematerials for the diluent include fluoride compounds such as LiF, MgF₂,CaF₂, SrF₂, AlF₃, K₂NaAlF₆, KMgF₃, CaLiAlF₆, K₂LiAlF₆, and K₂SiF₆, whichhave index of refraction ranging from about 1.38 (AlF₃ and K₂NaAlF₆) toabout 1.43 (CaF₂), and polymers having index of refraction ranging fromabout 1.254 to about 1.7. Non-limiting examples of polymers suitable foruse as a diluent include polycarbonates, polyesters, nylons,polyetherimides, polyetherketones, and polymers derived from styrene,acrylate, methacrylate, vinyl, vinyl acetate, ethylene, propylene oxide,and ethylene oxide monomers, and copolymers thereof, includinghalogenated and unhalogenated derivatives. These polymer powders can bedirectly incorporated into silicone encapsulants before silicone curing.

In yet another embodiment, phosphor composition 22 is coated onto asurface of the shell 18, instead of being formed over the LED chip 12.The phosphor composition is preferably coated on the inside surface ofthe shell 18, although the phosphor may be coated on the outside surfaceof the shell, if desired. Phosphor composition 22 may be coated on theentire surface of the shell or only a top portion of the surface of theshell. The UV/blue light emitted by the LED chip 12 mixes with the lightemitted by phosphor composition 22, and the mixed light appears as whitelight. Of course, the phosphor may be located in any two or all threelocations or in any other suitable location, such as separately from theshell or integrated into the LED.

FIG. 2 illustrates a second structure of the system according to thepresent invention. Corresponding numbers from FIGS. 1-4 (e.g. 12 inFIGS. 1 and 112 in FIG. 2) relate to corresponding structures in each ofthe figures, unless otherwise stated. The structure of the embodiment ofFIG. 2 is similar to that of FIG. 1, except that the phosphorcomposition 122 is interspersed within the encapsulant material 120,instead of being formed directly on the LED chip 112. The phosphor (inthe form of a powder) may be interspersed within a single region of theencapsulant material or throughout the entire volume of the encapsulantmaterial. Radiation (indicated by arrow 126) emitted by the LED chip 112mixes with the light emitted by the phosphor 122, and the mixed lightappears as white light 124. If the phosphor is to be interspersed withinthe encapsulant material 120, then a phosphor powder may be added to apolymer precursor, and loaded around the LED chip 112. The polymer orsilicone precursor may then be cured to solidify the polymer orsilicone. Other known phosphor interspersion methods may also be used,such as transfer molding.

FIG. 3 illustrates a third possible structure of the system according tothe present invention. The structure of the embodiment shown in FIG. 3is similar to that of FIG. 1, except that the phosphor composition 222is coated onto a surface of the envelope 218, instead of being formedover the LED chip 212. The phosphor composition 222 is preferably coatedon the inside surface of the envelope 218, although the phosphor may becoated on the outside surface of the envelope, if desired. The phosphorcomposition 222 may be coated on the entire surface of the envelope, oronly a top portion of the surface of the envelope. The radiation 226emitted by the LED chip 212 mixes with the light emitted by the phosphorcomposition 222, and the mixed light appears as white light 224. Ofcourse, the structures of FIGS. 1-3 may be combined, and the phosphormay be located in any two or all three locations, or in any othersuitable location, such as separately from the envelope, or integratedinto the LED.

In any of the above structures, the lamp may also include a plurality ofscattering particles (not shown), which are embedded in the encapsulantmaterial. The scattering particles may comprise, for example, alumina ortitania. The scattering particles effectively scatter the directionallight emitted from the LED chip, preferably with a negligible amount ofabsorption.

As shown in a fourth structure in FIG. 4, the LED chip 412 may bemounted in a reflective cup 430. The cup 430 may be made from or coatedwith a dielectric material, such as alumina, titania, or otherdielectric powders known in the art, or be coated by a reflective metal,such as aluminum or silver. The remainder of the structure of theembodiment of FIG. 4 is the same as those of any of the previousfigures, and can include two leads 416, a conducting wire 432, and anencapsulant material 420. The reflective cup 430 is supported by thefirst lead 416 and the conducting wire 432 is used to electricallyconnect the LED chip 412 with the second lead 416.

Another structure (particularly for backlight applications) is a surfacemounted device (“SMD”) type light emitting diode 550, e.g. asillustrated in FIG. 5. This SMD is a “side-emitting type” and has alight-emitting window 552 on a protruding portion of a light guidingmember 554. An SMD package may comprise an LED chip as defined above,and a phosphor material that is excited by the light emitted from theLED chip. Other backlight devices include, but are not limited to, TVs,computers, smartphones, tablet computers and other handheld devices thathave a display including a semiconductor light source; and a colorstable Mn⁴⁺ doped phosphor according to the present invention.

When used with an LED emitting at from 350 to 550 nm and one or moreother appropriate phosphors, the resulting lighting system will producea light having a white color. Lamp 10 may also include scatteringparticles (not shown), which are embedded in the encapsulant material.The scattering particles may comprise, for example, alumina or titania.The scattering particles effectively scatter the directional lightemitted from the LED chip, preferably with a negligible amount ofabsorption.

In addition to the color stable Mn⁴⁺ doped phosphor, phosphorcomposition 22 may include one or more other phosphors. When used in alighting apparatus in combination with a blue or near UV LED emittingradiation in the range of about 250 to 550 nm, the resultant lightemitted by the assembly will be a white light. Other phosphors such asgreen, blue, yellow, red, orange, or other color phosphors may be usedin the blend to customize the white color of the resulting light andproduce specific spectral power distributions. Other materials suitablefor use in phosphor composition 22 include electroluminescent polymerssuch as polyfluorenes, preferably poly(9,9-dioctyl fluorene) andcopolymers thereof, such aspoly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine)(F8-TFB); poly(vinylcarbazole) and polyphenylenevinylene and theirderivatives. In addition, the light emitting layer may include a blue,yellow, orange, green or red phosphorescent dye or metal complex, or acombination thereof. Materials suitable for use as the phosphorescentdye include, but are not limited to, tris(1-phenylisoquinoline) iridium(III) (red dye), tris(2-phenylpyridine) iridium (green dye) and Iridium(III) bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue dye).Commercially available fluorescent and phosphorescent metal complexesfrom ADS (American Dyes Source, Inc.) may also be used. ADS green dyesinclude ADS060GE, ADS061GE, ADS063GE, and ADS066GE, ADS078GE, andADS090GE. ADS blue dyes include ADS064BE, ADS065BE, and ADS070BE. ADSred dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE, ADS076RE,ADS067RE, and ADS077RE.

Suitable phosphors for use in phosphor composition 22 include, but arenot limited to:

-   ((Sr_(1-z)(Ca, Ba, Mg, Zn)_(z))_(1-(x+w))(Li, Na, K,    Rb)_(w)Ce_(x))₃(Al_(1-y)Si_(y))O_(4+y+3(x-w))F_(1-y-3(x-w)),    0<x≤0.10, 0≤y≤0.5, 0≤z≤0.5, 0≤w≤x;-   (Ca,Ce)₃Sc₂Si₃O₁₂ (CaSiG);-   (Sr,Ca,Ba)₃Al_(1-x)Si_(x)O_(4+x)F_(1-x):Ce³⁺ (SASOF));-   (Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu²⁺,Mn²⁺; (Ba,Sr,Ca)BPO₅:Eu²⁺,Mn²⁺;-   (Sr,Ca)₁₀(PO₄)₆*νB₂O₃:Eu²⁺ (wherein 0≤ν≤1); Sr₂Si₃O₈*2SrCl₂:Eu²⁺;-   (Ca,Sr,Ba)₃MgSi₂O₈:Eu²⁺,Mn²⁺; BaAl₈O₁₃:Eu²⁺;    2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺;-   (Ba,Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺; (Ba,Sr,Ca)Al₂O₄:Eu²⁺;    (Y,Gd,Lu,Sc,La)BO₃:Ce³⁺,Tb³⁺;-   ZnS:Cu⁺,Cl⁻; ZnS:Cu⁺,Al³⁺; ZnS:Ag⁺,Cl⁻; ZnS:Ag⁺,Al³⁺;    (Ba,Sr,Ca)₂Si_(1-ξ)O_(4-2ξ):Eu²⁺ (wherein 0≤ξ≤0.2);    (Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu²⁺; (Sr,Ca,Ba)(Al,Ga,In)₂S₄:Eu²⁺;-   (Y,Gd,Tb,La,Sm,Pr,Lu)₃(Al,Ga)_(5-α)O_(12-3/2α):Ce³⁺ (wherein    0≤α≤0.5);-   (Ca,Sr)₈(Mg,Zn)(SiO₄)₄Cl₂:Eu²⁺,Mn²⁺; Na₂Gd₂B₂O₇:Ce³⁺,Tb³⁺;-   (Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu²⁺,Mn²⁺; (Gd,Y,Lu,La)₂O₃:Eu³⁺, Bi³⁺;-   (Gd,Y,Lu,La)₂O₂S:Eu³⁺,Bi³⁺; (Gd,Y,Lu,La)VO₄:Eu³⁺,Bi³⁺;    (Ca,Sr)S:Eu²⁺,Ce³⁺; SrY₂S₄:Eu²⁺;-   CaLa₂S₄: Ce³⁺; (Ba,Sr,Ca)MgP₂O₇:Eu²⁺,Mn²⁺; (Y,Lu)₂WO₆:Eu³⁺, Mo⁶⁺;-   (Ba,Sr,Ca)_(β)Si_(γ)N_(μ):Eu²⁺ (wherein 2β3+4γ=3μ);    Ca₃(SiO₄)Cl₂:Eu²⁺;-   (Lu,Sc,Y,Tb)_(2-u-v)Ce_(v)Ca_(1+u)Li_(w)Mg_(2-w)P_(w)(Si,Ge)_(3-w)O_(12-u/2)    (where −0.5≤u≤1, 0<v≤0.1, and-   0≤w≤0.2); (Y,Lu,Gd)_(2-φ)Ca_(φ)Si₄N_(6+φ)C_(1-φ):Ce³⁺, (wherein    0≤□≤0.5); (Lu,Ca,Li,Mg,Y),-   α-SiAION doped with Eu²⁺ and/or Ce³⁺; (Ca,Sr,Ba)SiO₂N₂:Eu²⁺,Ce³⁺;    β-SiAlON:Eu²⁺,-   3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺; Ca_(1-c-f)Ce_(c)Eu_(f)Al_(1+c)Si_(1-c)N₃,    (where 0≤c≤0.2, 0≤f≤0.2);-   Ca_(1-h-r)Ce_(h)Eu_(r)Al_(1-h)(Mg,Zn)_(h)SiN₃, (where 0≤h≤0.2,    0≤r≤0.2); Ca_(1-2s-t)Ce_(s)(Li,Na)_(s)Eu_(t)AlSiN₃,-   (where 0≤s≤0.2, 0≤t≤0.2, s+t>0); and (Sr,Ca)AlSiN₃:Eu²⁺,Ce³⁺.

Phosphor composition 22 may additionally or alternatively includequantum dot (QD) phosphors or QD materials that emit in any color. Inparticular, QD materials for use in phosphor composition 22 include atleast one population of QDs capable of emitting green light uponexcitation by a blue light source. The QD wavelengths and concentrationscan be adjusted to meet the optical performance required. Preferred QDcharacteristics include high quantum efficiency (e.g., about 90% orgreater), continuous and tunable emission spectrum, and narrow and sharpspectral emission, e.g., less than 50 nm, 30 nm or less, or 20 nm orless full width at half max (FWHM).

The quantum dot material may include a group II-VI compound, a group IIIV compound, a group IV-IV compound, a group IV compound, a groupI-III-VI₂ compound or a mixture thereof. Non-limiting examples of groupII-VI compounds include CdSe, CdTe, CdS, ZnSe, ZnTe, ZnS, HgTe, HgS,HgSe, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS,CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS,CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe,HgZnSTe, or combinations thereof. Group III-V compounds may be selectedfrom the group consisting of GaN, GaP, GaAs, AlN, AlP, AlAs, InN, InP,InAs, GaNP, GaNAs, GaPAs, AlNP, AlNAs, AlPAs, InNP, InNAs, InPAs,GaAlNP, GaAlNAs, GaAlPAs, GaInNP, GaInNAs, GaInPAs, InAlNP, InAlNAs,InAlPAs, and combinations therof. Examples of group IV compounds includeSi, Ge, SiC, and SiGe. Examples of group I-III-VI₂ chalcopyrite-typecompounds include CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂, AgInS₂, AgInSe₂,AgGaS₂, AgGaSe₂ and combinations thereof.

QDs for use in phosphor composition 22 may be a core/shell QD, includinga core, at least one shell coated on the core, and an outer coatingincluding one or more ligands, preferably organic polymeric ligands.Exemplary materials for preparing core-shell QDs include, but are notlimited to, Si, Ge, Sn, Se, Te, B, C (including diamond), P, Co, Au, BN,BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs,InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe,CdS, CdSe, CdSeZn, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe,MnS, MnSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF,CuCl, CuBr, CuI, Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga, In)₂ (S, Se, Te)₃, Al₂CO,and appropriate combinations of two or more such materials. Exemplarycore-shell QDs include, but are not limited to, CdSe/ZnS, CdSe/CdS,CdSe/CdS/ZnS, CdSeZn/CdS/ZnS, CdSeZn/ZnS, InP/ZnS, PbSe/PbS, PbSe/PbS,CdTe/CdS and CdTe/ZnS.

The QD materials typically include ligands conjugated to, cooperatedwith, associated with, or attached to their surface. In particular, theQDs may include a coating layer comprising ligands to protect the QDsfrom environmental conditions including elevated temperatures, highintensity light, external gasses, and moisture, control aggregation, andallow for dispersion of the QDs in the matrix material.

The ratio of each of the individual phosphors in the phosphor blend mayvary depending on the characteristics of the desired light output. Therelative proportions of the individual phosphors in the variousembodiment phosphor blends may be adjusted such that when theiremissions are blended and employed in an LED lighting device, there isproduced visible light of predetermined x and y values on the CIEchromaticity diagram. As stated, a white light is preferably produced.This white light may, for instance, may possess an x value in the rangeof about 0.20 to about 0.55, and a y value in the range of about 0.20 toabout 0.55. As stated, however, the exact identity and amounts of eachphosphor in the phosphor composition can be varied according to theneeds of the end user. For example, the material can be used for LEDsintended for liquid crystal display (LCD) backlighting. In thisapplication, the LED color point would be appropriately tuned based uponthe desired white, red, green, and blue colors after passing through anLCD/color filter combination.

LED devices incorporating the color stable phosphors and used forbacklighting or general illumination lighting may have a color shift of<1.5 MacAdam ellipses over 2,000 hours of device operation, and, inparticular embodiments, <1 MacAdam ellipse over 2,000 hours, where thephosphor/polymer composite is in direct contact with the LED chipsurface, LED wall plug efficiency greater than 40%, and LED currentdensities are greater than 2 A/cm². In accelerated testing, where thephosphor/polymer composite is in direct contact with the LED chipsurface, LED wall plug efficiency greater than 18%, and LED currentdensities are greater than 70 A/cm², LED devices may have color shift of<1.5 MacAdam ellipse over 30 minutes.

The color stable Mn⁴⁺ doped phosphors of the present invention may beused in applications other than those described above. For example, thematerial may be used as a phosphor in a fluorescent lamp, in a cathoderay tube, in a plasma display device or in a liquid crystal display(LCD). The material may also be used as a scintillator in anelectromagnetic calorimeter, in a gamma ray camera, in a computedtomography scanner or in a laser. These uses are merely exemplary andintended to be not limiting.

EXAMPLES Comparative Examples 1-2

A treatment solution composed of K₂SiF₆ dissolved in 49% HF was preparedby adding 4.2 g K₂SiF₆ per 100 ml 49% HF to form a suspension which wasvacuum filtered to remove excess solids. Approximately 2 vol % 49% HFwas added to the saturated solution, to form a nearly saturatedsolution.

Samples of Mn-doped potassium fluorosilicate phosphor, K₂SiF₆:Mn wereadded to separate treatment solution at a rate of about 6 ml solutionper 1 g product and stirred for about 20 minutes. The treated productwas vacuum filtered, rinsed once with acetic acid and three times withacetone, and then dried under vacuum. The dried powder was siftedthrough a 170-mesh screen, and annealed under an atmosphere composed of20% F₂/80% nitrogen for about 8 hours at 540° C.

The annealed phosphor was mixed with treatment solution of 49% HF nearlysaturated with K₂SiF₆ at a rate of about 12 ml solution per 1 g productand stirred for about 20 minutes. The treated product was vacuumfiltered, rinsed once with acetic acid and three times with acetone, andthen dried under vacuum. The dried powder was sifted through a 170-meshscreen.

Examples 1 and 2

The treated phosphors of Comparative Examples 1 and 2 were placed in acontainer composed of a fluoropolymer and annealed at 90° C. for 8 hoursunder a 20% F₂/80% nitrogen atmosphere.

Tapped bulk density of the phosphors of Examples 1 and 2 and ComparativeExamples 1 and 2 was determined by tapping a vessel containing thephosphor and measuring the volume of the powder. Particle size data wasobtained using a Horiba LA-960 Laser Scattering Particle SizeDistribution Analyzer. Tapped bulk density data, quantum efficiency,lifetime, and particle size distribution for the products is shown inTable 1.

bulk % Rel d10/d50/d90 density density QE, particle size, Example no.sample ID (g/mL) decrease % Lifetime (ms) μm Comparative Ex. 1 C072215A-0.75 6.4% 103.7 8.449 17/28/47 TGAT(133) Example 1 C072215A- 0.70 103.88.45 16/28/49 TGATA(134) Comparative Ex. 2 C072215B- 0.77 6.5% 103 8.45415/24/37 TGAT(133) Example 2 C072215B- 0.72 103.1 8.445 14/22/33TGATA(134)It can be seen that the phosphors of Examples 1 and 2 had lower bulkdensity relative to those of Comparative Examples 1 and 2, while otherproperties remain constant. The drop in bulk density may be due to lessagglomeration of the particles which may result in improved deviceperformance.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A process comprising contacting a complexfluoride phosphor of formula I,A_(x)MF_(y):MN⁴⁺  I with a first fluorine-containing oxidizing agent ingaseous form at a first temperature ranging from greater than 200° C. toabout 700° C., to form a first product phosphor; contacting the firstproduct phosphor in particulate form with a solution of a compound offormula II in aqueous hydrofluoric acid,A_(x)MF_(y)  II to form a treated phosphor; and contacting the treatedphosphor with a second fluorine-containing oxidizing agent in gaseousform at a second temperature of less than 225° C.; wherein A isindependently at each occurrence Li, Na, K, Rb, Cs, or a combinationthereof; M independently at each occurrence is Si, Ge, Sn, Ti, Zr, Al,Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x isthe absolute value of the charge of the MF_(y) ion; and y is 5, 6 or 7.2. A process according to claim 1, wherein the first and secondfluorine-containing oxidizing agents are independently selected from F₂,HF, SF₆, BrF₅, NH₄HF₂, NH₄F, KF, AlF₃, SbF₅, ClF₃, BrF₃, KrF, XeF₂,XeF₄, NF₃, SiF₄, PbF₂, ZnF₂, SnF₂, CdF₂, C₁-C₄ fluorocarbons, andcombinations thereof.
 3. A process according to claim 1, wherein each ofthe first and second fluorine-containing oxidizing agent is F₂.
 4. Aprocess according to claim 1, wherein M independently at each occurrenceis Si, Ge, Sn, Ti, Zr, or a combination thereof.
 5. A process accordingto claim 1, wherein A independently at each occurrence is Na, K, Rb, Cs,or a combination thereof; M independently at each occurrence is Si, Ge,Ti, or a combination thereof; and y is
 6. 6. A process according toclaim 1, wherein the complex fluoride phosphor is K₂SiF₆:Mn⁴⁺.
 7. Aprocess according to claim 1, wherein the compound of formula II isK₂SiF₆.
 8. A process according to claim 1, wherein the first temperatureis any temperature in a range from about 350° C. to about 700° C.
 9. Aprocess according to claim 1, wherein the second temperature is anytemperature in a range less than 225° C.
 10. A process according toclaim 1, wherein the second temperature is any temperature in a rangeless than 100° C.
 11. A process according to claim 1, wherein the secondtemperature is about 90° C.
 12. A process according to claim 1, whereinthe treated phosphor is contacted with the second fluorine-containingoxidizing agent for a period of about eight hours.
 13. A processaccording to claim 1, wherein the treated phosphor is contacted with thesecond fluorine-containing oxidizing agent for a period of about eighthours at a temperature of about 90° C.
 14. A process according to claim1, wherein the treated phosphor is contained in a vessel having anon-metallic surface during contact with the second fluorine-containingoxidizing agent.
 15. A process according to claim 14, wherein thenon-metallic surface comprises a fluoropolymer.